Building board

ABSTRACT

A SELF-SUPPORTING, LOAD BEARING BUILDING BOARD THAT IS RELATIVELY LIGHT IN WEIGHT AND ECONOMICAL TO MANUFACTURE AND USE. THE BOARD HAS MULTI-LAYERED CONSTRUCTION WITH A CENTRAL CORE OF RELATIVELY STRONG FORAMINOUS MATERIAL, INTERMEDIATE LAYERS OF A DIFFERENT MATERIAL MECHANICALLY BONDED TO THE OPPOSITE FACES OF THE CORE AND OUTER LAYERS OF FIBROUS MATERIAL BONDED TO THE INTERMEDIATE LAYERS. THE INTERMEDIATE LAYERS ARE CONSIDERABLY MORE DENSE THAN THE CORE MATERIAL AND HAVE SUFFICIENT COMPRESSION STRENGTH TO IMPART DIMENSIONAL STABILITY THERETO. THE OUTER LAYERS ARE IN TENSION AND INSURE A LASTING BOND BETWEEN THE INTERMEDIATE LAYERS AND CORE.

' p 12, 1972 J. w. ELISCHER 3,691,003

BUILDING BOARD Filed Nov. 23, 1970 INVENTOR. JULIUS W. ELZSCHE?ATTORNEYS United States Patent 3,691,003 BUILDING BOARD Julius W.Elischer, Nedlands, Western Australia, Australia Continuation-impart ofabandoned application Ser. No. 869,392, Oct. 24, 1969. This applicationNov. 23, 1970, Ser. No. 91,709

Int. Cl. B32b 3/26, 5/18, 13/08 US. Cl. 161--159 7 Claims ABSTRACT OFTHE DISCLOSURE A self-supporting, load bearing building board that isrelatively light in weight and economical to manufacture and use. Theboard has a multi-1ayered construction with a central core of relativelystrong foraminous material, intermediate layers of a different materialmechanically bonded to the opposite faces of the core and outer layersof fibrous material bonded to the intermediate layers. The intermediatelayers are considerably more dense than the core material and havesutficient compression strength to impart dimensional stability thereto.The outer layers are in tension and insure a lasting bond between theintermediate layers and core.

BACKGROUND OF THE INVENTION This application is a continuation-in-partof application Ser. No. 869,392, filed Oct. 24, 1969, now abandoned, bythe applicant herein.

The invention relates generally to structural building boards or panels,and has particular reference to an improved self-supporting, loadbearing building board of laminar construction.

In building construction, load bearing walls have traditionally beenbuilt of poured concrete, concrete blocks, bricks or the like. For manyyears, however, there has been a demand for cheaper and lighter wallconstructions, and of the many that have been developed the cheapest andmost widely used today, particularly for interior walls, is the stud andplaster board wall which has largely supplanted the rendered stud-lathwall. Because of the popularity of the stud and plaster board wall,there have been a large number of additional developments directedtoward improving plaster or wallboards per se.

Another significant approach to light wall construction-aimed ateliminating the triple layer application of the stud and plaster boardwallhas been the development of self-supporting prefabricated panels,usually laminated, which in and of themselves form the wall. Thoughintended to be self-supporting, many of these have or develop a slightbend, and most are not accepted by building authorities as load bearingor permanent structures. In addition, most prefabricated panelsdeveloped heretofore lack dimensional stability and have inferiorfireproofing and soundproofing characteristics. Those panels that do nothave these drawbacks are usually too expenesive for ordinary use.

SUMMARY OF THE INVENTION The present invention is directed to a greatlyimproved prefabricated building board that is self-supporting and loadbearing, and particularly adapted for use in constructing nonmodular,flush walls and ceilings. Compared with conventional plaster board, thisprefabricated board is relatively thick, although for normalapplications it is less thick than a stud and plaster board wall and fareasier to erect. The board is comprised of five layers including arelatively thick central core of foamed hydraulic cement which islightweight and yet provides structural strength.

Mechanically bonded to the opposite faces of the core are layers ofplaster having sufiicient compression strength to insure that the core,and thus the board as a whole, will have dimensional stability as toheight and width. Outer layers of relatively heavy paper are bonded tothe outside faces of the plaster layers, the paper layers forming anexternal tensile skin for the board. The paper being under tensionserves to insure a lasting bond between the plaster layers and cellularcore, and enables a flush joint between adjacent boards by sealing thejoint in the same way that joints between conventional plaster boardsare sealed. The building boards of the invention do not have, and do notrequire for support, a surrounding frame of any kind as in a modulartype panel, such frames making it difficult to conceal the joints in themanner desired for non-modular, flush walls and ceilings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a fragmentary transversesection through a pair of adjacent building boards embodying theinvention, in a non-modular flush wall construction; and

FIG. 2 is a diagrammatic side elevation of an apparatus for making theboards and illustrating the manner in which a board is fabricated.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings,and with particular reference to FIG. 1, the building board of theinvention is indicated generally at 4 and comprises a central core 6 offoamed hydraulic cement, specifically portland cement, a pair ofintermediate layers of plaster 8 and a pair of outer layers 10 offibrous material such as heavy paper. The core is relatively thick toprovide structural strength and yet is considerably lighter than a slabof solid concrete or solid plaster of the same dimensions. In accordwith the invention, the core has a thickness of at least 1", and formost applications the thickness is preferably in the order of 1 /2".

The foamed cement is made by a well known process in which a foamingagent is added to a cement slurry. This material is initially cast inlarge blocks and the blocks are then cut up with a power saw to formslabs of the required thickness for the cores. The sawing opens up thecells in the opposite faces of the core, and the plaster 8 is appliedwet or in slurry form to these faces to form the intermediate layers. Inso doing, the plaster penetrates the open cells of the core slab andbecomes mechanically bonded thereto, the plaster being keyed to the slabat myriad points on the interfaces 12 of the core and plaster.

The plaster 8 in the embodiment disclosed is a gypsum plaster with acompression strength of not less than 2,200 lbs. per square inch. Itsprimary purpose in the building board is to impart dimensional stabilityto the foamed cement core and thus to the board as a whole. The plasteris per se dimensionally stable whereas the core material is not; thefoamed concrete retains a tendency to shrink even though well cured, andif it were used alone as a building panel cracks would soon appeareverywhere the panel joined any other part of the structure. However, ithas been found that by cutting open the cells on the opposite faces ofthe foraminous core and then filling them with the dimensionally stableplaster, shrinkage does not occur in the planes of the faces i.e., withrespect to the height and Width of the board. Some shrinkage .may stilloccur perpendicular to the faces, affecting the thickness of the board,but since this dimension is small compared with the height and widthdimensions, the shrinkage is minimal and its effect is negligible.

In order to have the intermediate plaster layers 8 function as intended,the layers must not be too thin. On the other hand, it is notadvantageous to have them too thick as this would only add unnecessaryand undesirable weight to the board. In all cases, the compressionstrength of the plaster layers must be greater than the forces tendingto shrink the core, and using plaster having a compression strength of2,200 lbs. per square inch, it has been determined that the layerthickness should be from /8" to with a thickness of A" being preferredfor a 1 /2" thick core.

The outer layers 10 of paper or lining board are applied to theintermediate plaster layers while the latter are wet, in a manner to bedescribed, and when the plaster dries the paper shrinks and thus isplaced under tension. The paper that is used has relatively high tensilestrength and its most important function is to insure a lasting bondbetween the core and plaster layers. If, for example, a core withplaster layers but no paper is subjected to a substantial impact or astress tending to bend the core, there is a tendency for the plaster tobreak away from the core even though there is a strong mechanical bond.The paper layers under tension effectively prevent this.

For the paper layers to function in the desired manner, the physicalcharacteristics thereof must be balanced with those of the plasterlayers. Thus, the paper must be capable of being placed under enoughtension to keep the plaster firmly bonded to the core but the tensioncannot be so great as to crumble or otherwise damage the plaster layers.It has been found that paper in the 74-86 lb. range meets thesequalifications with a 76 lb. paper & thick being preferable for plasterlayers having the characteristics described above.

In addition to its function of maintaining a firm bond between the coreand plaster layers, the paper protects the plaster against chipping andscratching during handling and enables a continuous, flush skin to beformed in the manner desired for non-modular construction. To this end,the paper and plaster layers may be slightly recessed adjacent the edgesof each board as indicated at 14 to accommodate a joining strip 16 ofpaper or gauze, the strip being secured in position in a known manner byplaster or a suitable adhesive. As will be apparent, the paper skin isalso well adapted to receive a finishing surface such as paint orwallpaper.

The five-layered building board of the invention preferably has aminimum thickness of 2" which, of course, is considerably thicker thanconventional thick plaster board. However, unlike plaster board, theprefabricated boards disclosed herein are in and of themselvesselfsupporting and load bearing. Moreover, the overall thickness of theboards is less than the overall thickness of a wall comprised of studsand two sheets of plaster board.

In order to obtain a board that is relatively light in weight, asubstantial part of the board must consist of a lightweight material andthe foamed hydraulic cement has the most desirable characteristics forthis purpose. In addition to being lightweight, this material isinexpensive, stronger than foamed plaster or foamed synthetic resins andhas good fireproofing and soundproofing properties. Also, the plasterlayers can be securely bonded to it without the need for glue or othersupplemental means. In certain instances, as for example for ceilingpanels and in certain wall installations, wood-wool cement orpolystyrene can be substituted for the foamed cement although for mostapplications the latter is the preferred core material.

In order to effect a suitable compromise between lightness and strength,the density of the foamed cement should be from 25 to 40 lbs. per cubicfoot and preferably is in the order of 28-30 lbs. per cubic foot. A slabof foamed cement with this density and a thickness of at least 1 ascontemplated by the invention has structural strength and substantialresistance to shear loads. Such a slab, on the other hand, has by itselfrelatively little strength in tension and compression and, as notedabove, is usually not dimensionally stable. With the high compressionstrength plaster layers bonded to the foamed cement core in the mannerdescribed above the core is, however, made dimensionally stable.

With the construction disclosed herein, there is provided a buildingboard with outer layers in tension, intermediate layers in compressionand a central core with structural strength and substantial resistanceto shear loads. The layers in the combination and with the materialsdescribed cooperate in such a way that the resultant board hasstructural strength that exceeds by far the structural strength of anyof its individual components and, at the same time, is lightweight anddimensionally stable. With such a construction, the term self-supportingas used herein is intended to mean that the building board of theinvention will stand upright, or span the distance between supports in aceiling, without bending or sagging and without additional support meanssuch as a frame or external structural members. The term load bearing asapplied to the building board is intended to mean that a partition wallconstructed from the board will aid in supporting building structureabove and bearing on it.

In a particular embodiment of the invention, given as an example, thecentral core 6 is foamed hydraulic cement 1 /2" thick and having adensity of 28-30 lbs. per cubic ft. The intermediate plaster layers 8are gypsum plaster having a compression strength of 2,200 lbs. persquare inch and a thickness of A". The outer layers 10 are 76 lb. paperthat is thick. In this specific example, the overall width of the boardis 2 and the ratio of the core thickness to the thickness of one of theplaster layers is 6:1. The substantially greater thickness of the core,in addition to providing strength and shear resistance, serves toprovide ample spacing between opposite compression and tension layerswhich permits these layers to contribute more effectively to the overallstrength of the board than if they were close together.

FIG. 2 diagrammatically illustrates apparatus for fabricating thebuilding board. With this apparatus, a preformed, cured slab 6 of foamedcement is fed by suitable conveyor means (not shown) between a pair ofendless belts 18, 20 supported by rollers 22. As the slab moves fromleft to right, plaster 8' in plastic or slurry form is deposited on theopposite faces of the slab by hoppers 24, 26, the lower hopper 26 firstdepositing the plaster on a web of paper 10' which is paid out from asuitably supported roll 28. In this manner, the paper overlies theplaster on the underside of the slab. Another web of paper 10' is paidout from an upper roll 30 so that it overlies the plaster deposited onthe upper side of the slab. The rollers 32, together with rollers 22,spread the plaster into layers of uniform thickness and also force itinto the open cells of the slab. At the same time, the rollers press thepaper layers 10' into close contact with the plaster layers.

In the building board of the invention, the core must be prefabricatedor pre-formed because it is too thick to be formed simultaneously withthe plaster layers in a so-called wet process such as is used inmanufacturing plaster boards. Thus, the wet process is limited torelatively thin boards, less than 1 in thickness, because the layer orlayers of plastic material that go into the board must be thin enough toset up quickly. In addition, the wet process does not work well wherethe layers are of different materials as in the present invention.

From the foregoing description, it will be apparent that the inventiondisclosed herein provides a greatly improved prefabricated buildingboard having substantial advantages over previously developed boards ofthis type. As will be understood by those familiar with the art, theinvention may be embodied in other specific forms without departing fromthe spirit or essential characteristics thereof.

I claim:

1. A self-supporting, load bearing, frameless building board comprisinga central core in the form of a slab of foamed cement having a thicknessof at least one inch, an

intermediate plaster layer of high compression strength mechanicallybonded to each opposite face of the central core by penetration into theinterstitial spaces therein, and an outer pretensioned layer of paper ofhigh tensile strength securely bonded to each intermediate plasterlayer.

2. A building board as defined in claim 1 wherein the board has athickness of at least 2", and each plaster layer is from Ma" to thick.

3. A building board as defined in claim 1 wherein the density of thefoamed cement core is in the range of 25- 40 lbs. per cubic foot.

4. A building board as defined in claim 1 in which the strength of theplaster layers in compression exceeds the tensile strength of the foamedconcrete core whereby the intermediate plaster layers counteract thetendency of the core material to shrink.

S. A building board as defined in claim 4 wherein the plaster layers arecomprised of gypsum plaster having a compression strength of not lessthan 2,200 lbs. per square inch.

6. A self-supporting, load bearing building board having an overallthickness of at least 2" and comprising a central core of foraminousmaterial having a thickness of at least 1", the core being a pre-formedslab having a multiplicity of open cells on the opposite faces thereof,an intermediate plaster layer mechanically bonded to each opposite faceof the core by penetration of the plaster into the open cells therein,the plaster forming the intermediate layers having a compressionstrength of not less than 2,200 lbs. per square inch, and an outerpretensioned layer of paper of high tensile strength securely bonded toeach intermediate plaster layer, the paper in the outer layers being inthe range of 74-86 lbs.

7. A building board as defined in claim 6 wherein the thickness of thecentral core is at least six times the thickness of one of the plasterlayers.

References Cited UNITED STATES PATENTS 1,875,364 9/1932 Armstrong 1611612,721,369 10/1955 Burke 52-612 X 3,269,071 8/ 1966 Johnson 52-612 X3,295,278 1/1967 Muhm 52--612 X FOREIGN PATENTS 211,635 8/1956 Australia52-612 WILLIAM A. '"POWELL, Primary Examiner US. Cl. XJIR.

